Dwyer Mark II - Manual (Page 2)

AIR VELOCITY CALCULATIONS:
Air Velocity = 1096.2
where Pv = velocity pressure in inches of water
D = Air density in lb/ft 3
Air Density = 1.325 x
where PB = Barometric Pressure in inches of mercury
T = Absolute Temperature (indicated temperature °F plus
460)
Flow in cu. ft. per min. = Duct area in square feet x air velocity
in ft. per min.
AIR FILTER GAGE
Mount gage within 3 ft. of filter bank. Install tubing adapters on
each side of filter. Run tubing from clean side of filter to positive
pressure side of gage (left fitting). Run downstream side to low
pressure side of gage (right fitting). Install green and red arrows
adjacent to indicating tube to indicate filter condition.
AIR VELOCITY METER
A pitot tube should be used for air velocity readings. Install the
pitot tube and gage carefully to ensure accuracy. Select a
location for the pitot tube with al least four diameters of smooth
straight sections of duct both upstream and downstream. Install
pitot tube in the center of duct with tip directed into air stream.
Connect the right angle (leg parallel to tip) to negative (right
fitting) and straight pitot tube connection to positive (left
connection) of gage. The velocity reading shown on the gage is
the center or maximum velocity. For average velocity across the
full area, multiply by a factor of 0.9.
No’s. 27 and 28 require pitot tube at additional cost. See Bulletin
F-41-F.
The velocity indicated is for dry air at 70°F, 29.9˝ barometric
pressure and a resulting density of 0.075 lb/ft
3 . For variation from
these standard conditions, corrections may be based upon the
following data.
FLOW
Ps Pt
PITOT TUBE
(SECTION
ENLARGED
TO SHOW
DETAIL)
APPLICATIONS MARK II MANOMETER
PITOT TUBE SENSES TOTAL AND STATIC PRESSURES. MANOMETER
MEASURES VELOCITY PRESSURE-(DIFFERENCE BETWEEN TOTAL AND
STATIC PRESSURES).
P V
D
√
P B
T